Mary was born to Emelyne Reid and Aubrey Reid. She was quite close to her older brother Jonathan. At one point in her life she got married and gave birth. However, the war and the flu epidemic took her happiness away as her husband was killed in France during the war and her child died due the flu. Mary only soles was the hope that her brother will return just like he promise her in the letters he kept send her.
Events of VAMPYR
On the night of her brother's disappearance, Mary went out in search of Reid. She entered the Southwark district and began to call out for him. A recently turned Reid found his way to his sister, listening to her heartbeat. Mary, unaware of her brother's condition, embraced him, glad to see him alive.
Reid, overcome with thirst, bites his sister and drains her of her blood. With her last breath, Mary asked her brother what he had done to her. Reid attempted to get help for Mary, but he was forced to flee when Vampire hunters began shooting at him.
Following her death, she was buried in a quarantined graveyard outside of the Whitechapel district. Her mother and their manservant, Avery, attended while Father Joseph oversaw her burial. After the funeral proceedings were completed, Reid visited Father Joseph at the Saint Mary's Church, where he openly admitted that he was responsible for her death.